1. Field of the Invention
The present invention relates to a rod antenna control system for automobiles with a motor-driven mechanism to push up an antenna rope to extend a rod antenna for an automobile.
2. Prior Art
In order to extend and retract a rod antenna for an automobile, an antenna rope made of nylon, etc. is often used. One end of the rope is connected to the tip of a rod antenna, and the rope is driven by a motor so as to be pushed up and down so that the antenna rod is extended and retracted.
In this type of conventional system, however, the antenna cannot be easily extended when it is covered with ice during icy season. Accordingly, the system is designed so that a push-up power above a predetermined value can be exerted so as to assure that the antenna can be extended. In other words, the system uses a motor which is capable of insuring sufficient amount of push-up power even if the voltage of the automobile battery, which is normally 12 V, decreases to about 9 V.
However, when the voltage of the battery is raised to 16 V, for example, a problem would occur in that a very great push-up force is applied to the antenna rope, causing the antenna rope to buckle and break when the rod antenna reaches its highest position.
In other words, since the power applied to the motor increases in proportion to the square of the voltage and the antenna push-up power also increases in proportion to the square of the voltage, the antenna rope ends up buckling and eventually breaking during a voltage surge to, for example, 16 volts.